The particulate fertilizers found available commercially can be produced and marketed in different types such as granules, pellets, ducts, piled or prilled. The fertilizers are generally formed of inorganic substances or organic substances or even a combination thereof.
In order to effectively promote plant growth, the fertilizers have to contain a certain amount of the water-soluble plant nutrients. Some of the typical major water-soluble plant nutrients include compounds of nitrogen, phosphorus, potassium which are often used in conjunction with other elements such as calcium, boron, magnesium, zinc, chloride and others.
Uncoated fertilizers are functioned by their rapid release of the soluble plant nutrients, which would cause phyto-toxicity and rapid depletion of the plant nutrients via leaching. Other problems would be the tendency of the uncoated fertilizers to form cake, create strong odor and become dusty.
As a result, much attempt is driven to overcome the defects caused by the uncoated fertilizers. The fertilizers are provided with coatings or encapsulations aiming for slow release of the plant nutrients.
There are some prior arts relating to encapsulated or coated fertilizers and their several production methods thereof.
A U.S. Pat. No. 6,358,295 discloses a method for producing granular coated fertilizer comprising the steps of adding a water-absorptive polymer to a granular fertilizer, placing the granular fertilizer in a tumbled state, adding liquid uncured urethane resin to the tumbled granular fertilizer in an amount enough to secure a desired of thickness, coating the surface of each granular fertilizer in the uncured urethane resin while keeping the granular fertilizer in the tumbled state and curing thermally the urethane resin while keeping the granular in tumbled state to form a urethane resin layer. The production steps are repeated at least one time. The water-absorptive polymer is acrylate polymer.
A process for producing polyurethane encapsulated, slow release fertilizer particles is described in another U.S. Pat. No. 6,358,296. The process comprising the steps of applying an isocyanate-reactive component onto fertilizer particles to form coated fertilizer particles wherein the isocyanate-reactive component comprises an oleo polyol and applying a polyisocyanate component unto the coated fertilizer particles to form polyurethane encapsulated fertilizer particles.
An European Patent No. 1551783 (published as WO 2004/011395) discloses a controlled release fertilizer material comprising a particulate plant nutrient surrounded by protective coating which comprises a particulate filler. A method of producing the controlled release fertilizer material is also described herein comprising the steps of contacting a particulate plant nutrient with a protective coating comprises a particulate filler material to surround the particulate plant nutrient.
A Canada Patent No. 1256710 claims a fertilizer composition in granular form having a regulated release of water-soluble fertilizer agents such as nitrogen, phosphorus, and potassium compounds. Each granule having a core comprising fertilizer substances, a coating encapsulating the core, wherein the coating is based on a dicyclopentadiene and linseed oil or a soybean oil alkyd to be served as a pH regulator. In the prior art, the coating comprises a first coating layer without any pH-regulating agent whereas a second coating layer around the first layer and including the pH-regulating agent.
The past existing polymer-coated fertilizers are not cost efficient and lack of sufficient abrasion resistance during handling, thus the fertilizers are easily agglomerate and have reduced slow release properties. Due to agglomeration which occurs between the encapsulated fertilizers, this would trigger sticky buildup of the fertilizers in the coating equipment which causes disruption in the continuous production and requires regular cleaning of the equipment.
To prevent the agglomeration of coated-fertilizers, either a filler such as barium sulfate or a methyl ester derivative of natural oil is used to decrease the viscosity of the coating material.
It is desirable to invent a controlled-release fertilizer that has improved abrasion resistance to avoid agglomeration and has efficient slow release of the plant nutrients. It is also desirable to invent a controlled-release fertilizer which has superior hydrophobic qualities by acquiring high content of natural oil polyol in the polyurethane coating.
Natural oil-based polyols are commonly known for their very strong hydrophobic properties due to the presence of long hydrocarbon chain. These hydrophobic properties offer a well protective coating to encapsulate the fertilizer particles and help to prevent the loss of nutrients. The use of natural oil-based polyol would also offer biodegradability to the coating material thus it is non-hazardous and could be digested by microorganisms.